Volatile matter yield

The above discussion has assumed that the rank of a coal can be adequately measured by a single parameter, such as the reflectance, the volatile matter yield or the organic carbon content. This assumption is commonly made, but it has for a long time appeared a pretty improbable proposition. The discussion also was restricted to bivariate correlations, that is, plots of a single variable against another. 

Thus the corrected volatile matter yield and the atomic H/C ratio both appear to be good parameters for assessing the reactivity of the coals studied. 

Thus a good correlation between conversion yield and one of these properties obviously implies a similar correlation with the other property. The correlations between the volatile matter yield and the reactive maceral content and between the H/C atomic ratio and the reactive maceral content are not statistically significant. 

Figure 3. Percentage conversion against volatile matter yield (hot rod mode)...

Figure 7. Percentage toluene solubles against H/C atomic ratio (X) and volatile matter yield (+)...

Figure 6. Dependence of maximum tar yields and corresponding total volatile matter yields during flash pyrolysis on atomic hydrogen-to-carbon ratio for some Australian and V.S.A. coals (O, 9), black coals (X), brown coals (A), Pittsburgh No. 8 (USA.) ( ), Montana lignite (USA).

Examination of ultrathin tactions of coal in tko aloctron microscope hat revealed that one type of vitrinite (vitrinite A) it homogeneous, while the remaining vitrinite (vitrinite B) it a two-component material, the components having similar properties to vitrinite A and exinite, respectively. The material similar to exinite occurs in sheets no more than 1000 A. thick and is responsible for the lower reflectance and higher volatile matter yield of vitrinite B. Exinite, micrinite, and semifusinite have been identified in ultrathin sections. By using a technique of impregnation with a lead salt the ultrafine pore structure of vitrinite has been made visible. 

The vitrinite without any sheets appears to correspond to what Brown, Cook, and Taylor (2) have called vitrinite A that with sheets appears to correspond to vitrinite B. The existence of this kind of laminar structure helps to explain the observation that vitrinite B has a higher volatile matter yield than vitrinite A although some of the coking properties of the two vitrinite types seem fairly similar. Many of the coking properties in fact appear to be primarily related to the matrix vitrinite. 

The classification of coal (ASTM D-388) depends on calculation of the volatile matter yield and fixed carbon values on a dmmf basis. Calorific values are calculated on a moist, mineral-matter-free basis. The Parr formula is used in the classification system to calculate the mineral matter from ash and sulfur data. 

The total volatile matter yield, and hence the yield of tar plus light oils, is proportional to the hydrogen-to-carbon ratio in the raw material. On the other hand, the chemically formed water vapor that distills off during pyrolysis in an inert atmosphere is proportional to the oxygen-to-carbon ratio. The yields and product distributions also depend on the rate of pyrolysis. 

For residence times below 0.15 s. Mg is more effective than Ca at reducing the yield of volatile matter. This may be due to the 30% higher Mg loading. In the total residence time of the reactor, however, Ca and Mg reduced the volatile matter yield equally. Tanabe ( 5) has reported Ca to be a better polymerization and/or cracking catalyst than Mg. The data in Figures 2 and 3 imply that in the... 

In addition, for similar loadings of Ca and Mg, 1.0 and 1.3 meq/g, respectively, the Ca loaded sample lost more weight than the Mg loaded sample for all residence times. This implies that for combustion, Ca has a dual advantage over Mg, First, at short residence times when pyrolysis dominates, volatile matter yield is higher. Second, at intermediate residence times, catalysis of the C-O2 reaction occurs. There is probably no advantage in the final char burnout stage, however. 

Coals generate the greatest volatile matter yield if heated to reaction temperature at very high rates to prevent cross-linking reactions that may reduce yield. Dilute-phase instead of dense-phase reactions may also enhance yield by eliminating secondary capture of cracked volatiles. This view is supported by laboratory studies. In flames, the chars formed after pyrolysis burn at rates dominated by internal chemical reaction, not diffusion, with reaction in zone I or zone II. At higher temperatures ( 2000°C) reaction in zone I is evidently first order with low activation energy (6 kcal/mole). At lower temperatures for zone /, E = 40 kcal/mole. Zone II yields E =20 kcal/mole with reaction order indeterminate but probably close to 0.5. 

The above analysis accounts qualitatively for the difference between fast and slow heating. Data are insufficient for an independent qualitative comparison, but the data of Figure 1 may be indicative. Here the volatile matter yield increases when the sample weight decreases if this is interpreted entirely as a Q factor, because of capture, the maximum increase possible is about 4 percentage points in 36%, giving a Q factor of 1.1. This... 

Figure 7 compares the influence of pyrolysis temperature on volatile matter yield for an Athabasca oil sand bitumen and a Utah... 

N.W. Asphalt Ridge formation) bitumen extract. These data were obtained from isothermal TG. The volatile matter yield was obtained by extrapolation of the instantaneous weight loss values to infinity under conditions wherein the pyrolysis rate approached a linear, steady-state value. The inset in Fig. 7 shows an example of such a plot. Data such as those shown in Fig. 7 are also useful in assessing the relative energy richness of a suite of oil sand samples at a given temperature. 

FIGURE 3.24 Variation of volatile matter yield with age of coal. (From Murchison, D. and Westoll, T.S., Eds., Coal and Coal Bearing Strata, Elsevier, New York, 1968.)... 

Coal rank from the petrographic point of view is commonly expressed in terms of vitrinite reflectance which may act as an indicator that is independent of other factors (e.g., coal type or grade). Unlike other chemical parameters (e.g., carbon content, hydrogen content, volatile matter yield, and calorific value) it is not dependent on the overall composition of the coal. A number of coal properties progressively change with the advance in rank and the rank of a coal is therefore a major factor influencing its potential application. 

Thus, the objective of the proximate analysis is to determine the amount moisture, volatile matter yield, ash yield, and fixed carbon from the coal sample. Mineral matter is not directly measured but may be obtained by one of a number of empirical formula either from the yield of mineral ash or from data derived from the ultimate analysis. 

FIGURE 9.7 Variation of coal strength with volatile matter yield. (From Brown, R.L. and Hiorns, F.J., Chemistry of Coal Utilization, Supplementary Volume, H.H. Lowry, Ed., John Wiley Sons, New York, 1963, Chapter 3.)... 

FIGURE 9.8 Variation of the hardgrove grindability index with volatile matter yield. (From Berkowitz, N.,... 

FIGURE 9.13 Variation of specific heat with volatile matter yield. (From Baughman, G.L., Synthetic Fuels Data Handbook, 2nd edn., Cameron Engineers, Inc., Denver, CO, 1978.)... 

The thermal conductivity of coal generally increases with an increase in the apparent density of the coal as well as with volatile matter yield, ash yield, and temperature. In addition, the thermal conductivity of the coal parallel to the bedding plane appears to be higher than the thermal conductivity perpendicular to the bedding plane. 

FIGURE 13.4 Relationship of volatile matter yield to heating rate. (From Eddinger, R.T. et al., Proceedings of the Seventh International Coal Science Conference, Prague, Czech Republic, 1968.)... 

FIGURE 13.5 Relationship of volatile matter yield to softening points and decomposition points of various coals. (From Gibson, J., Coal and Modern Coal Processing An Introduction. G.J. Pitt and G.R. Millward (Eds.), Academic Press, New York, 1979.)... 

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